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This invention relates generally to web handling apparatus and more particularly to a microprocessor controlled web guidance system to automatically implement and maintain proper lateral web alignment of a continuous web in a web handling system such as a printing press. In numerous industrial commercial processes, operations are performed in a continuous travelling web of a thin material, such as paper or plastic film, etc., which move through machines at high speed. Such web process operations include, for example, printing of newspapers or magazines, coating the moving web, slitting the moving web lengthwise, cutting the moving web transversely, etc. These operations usually require accurate lateral alignment of the web to maintain the web in proper registry with the machine that operates on the web. However, the moving web often shifts laterally from a proper lateral position on the rollers supporting it resulting in lateral misalignment relative to the machine. This displacement of the web from its proper lateral position interferes with the operations being performed on the web and often results in wastage and/or a crash of the web handling system. Thus, it is usually necessary to correct any misalignment as promptly as possible. Consequently, web guide devices which sense the lateral position of the web and automatically adjust the lateral position of the web when it deviates from a desired position are commonly used in the art.
It is known in the art to use web guide apparatus which includes a stationary support frame with a moveable steering frame mounted on the support frame. This moveable frame is steered by an appropriate positioning device such as a hydraulic cylinder or an electric motor, and normally includes a pair of spaced, parallel steering rollers over which the web is run. A sensor detects the lateral position of the web as it leaves the steering rollers and generates a signal to control the steering frame positioning motor. The moveable steering frame is pivoted relative to the support frame by the positioning motor about a pivot point along the center line axis of the incoming web. This pivoting action moves the rollers such that the web is repositioned laterally as it moves along and over the guide rollers.
In some prior art web guide apparatus, the sensing of the alignment of the moving head is accomplished by using a single web edge detector, such as a photodetector or infrared detector, positioned at one lateral edge of the moving web to detect transverse displacement of the web edge. In other situations, the width of the moving web may vary so that two edge detectors have been used to monitor both edges of the web. In addition, moveable edge detectors have been used in the prior art. Systems have also been proposed which provide a digital readout display of the correction being made to the position of the web.
Prior art web guide systems have numerous deficiencies. Such systems do not provide diagnostic and maintenance modes of operation to aide in the operation of the apparatus. Inability to calibrate the tilt mechanism makes it difficult to set trip points to stop or adjust the web handling line. These limitations often lead to undesirable and expensive crashes of the web handling line. In addition, control and drive mechanisms for the movement of the edge sensors has been inadequate leading to failure to keep track of sensor position and inaccurate position of the sensor due to gear backlash. The present invention overcomes these and other deficiencies of the prior art web guide apparatus and provides new and additional features not heretofore available.
Accordingly, it is an object of the present invention to provide a novel microprocessor controlled web guidance system having novel maintenance and diagnostic features.
It is another object of the invention to provide a novel microprocessor controlled web guidance system having a novel tilt mechanism calibration system for calibrating the full scale gain of the tilt mechanism.
It is yet another object of the invention to provide a novel microprocessor controlled web guidance system having a novel edge sensor drive mechanism utilizing a cogged linear belt in conjunction with stepper motors and counting means to keep track of the edge sensor position.
It is still another object of the invention to provide a novel microprocessor controlled web guidance system having a plurality of control panels with serial communications between the control panels and the control circuitry.
Briefly, according to one embodiment of the invention, a web guidance system is provided for automatically controlling alignment of a moving web. The system comprises a stationary support frame and a pivotable frame attached to the support frame and pivotable over a predetermined range, including parallel steering rollers for receiving the moving web. Sensing means is provided including at least one edge sensor positionable along either longitudinal edge of the web for sensing a transverse deviation in the position in the longitudinal edge of the web and for generating an error signal in response thereto. Control means is provided for generating a control signal responsive to the error signal for automatically correcting the deviation of the web position, and drive means is provided for controlling the angular position of said pivotable frame by pivoting the pivotable frame responsive to the control signals. In addition, manual means are provided to enable an operator to assume manual control of the drive means, and maintenance means provides maintenance modes of operation and can enable an operator to select functions and diagnostic, self-calibrating or maintenance modes of operation.